Cyclotrimerisation of Cyano-compounds into $1$,$3$,$5$-Triazines

A survey is made of papers on the cyclotrimerisation of substituted monofunctional cyanides $\mathrm{X}-\mathrm{C}\equiv\mathrm{N}$ differing in the structure of the substituent $\mathrm{X}=\mathrm{H}$, $\mathrm{R}$, $\mathrm{Ar}$, $>\!\!\mathrm{N}$, $\mathrm{HO}$, $\mathrm{RO}$, $\mathrm{ArO}$, $\mathrm{HS}$, $\mathrm{RS}$, $\mathrm{Hal}$. This reaction has been widely used in recent years both in preparative organic chemistry and in large-tonnage industrial manufactures, by virtue of the availability of the initial compounds, the high yields of $1$,$3$,$5$-triazines, and the simplicity of operation. Attention is paid mainly to recent work to elucidate the influence of substituents $\mathrm{X}$ on the reactivity of $\mathrm{N}\equiv\mathrm{C}$-containing compounds; various mechanisms of cyclotrimerisation are discussed, as well as the effects of catalysts, pressure, and other factors. Consideration is given not only to homocyclotrimerisation but also to mixed cyclotrimerisation of cyanide derivatives and the influence of the reaction conditions on the structure of the resulting $1$,$3$,$5$-triazines. A list of 247 references is included.